Preclinical and clinical studies of automated closed systems for positive and negative selection of lymphohematopoietic cells have been done in colla-boration with biotechnology firms that have developed systems for potential application to clinical cellular therapies. Nexell, Inc., Isolex: Studies of the automated Isolex 300i for immunomagnetic selec-tion of hematopoietic progenitor cells were continued, using system version 2.0. To date, over 100 selection procedures on version 2.0 (either positive only or combined positive/negative selection) have been completed. Studies of combined positive + negative selection aimed to achieve maximum T cell depletion of peripheral blood stem cell products have led to incorporation of this method into several allogeneic transplantation protocols. Current results show a mean CD3+ T cell depletion of 5 logs, with mean CD34+ cell recovery of 60 percent. Ongoing studies are aimed at evaluating new T cell antibodies (CD4, CD8, CD2) in the system. Evaluation of the next version of the system is anticipated to begin in July 1999. CellPro T Cell Depletion System: A clinical evaluation of this two-step positive (CD34) and negative (CD2) selection system, which uses an immunoadsorption approach, was completed in August 1998. This study randomized 24 allogeneic donors to fresh versus pooled processing of stem cell apheresis products. Results demonstrated equivalence between the two study arms in processing and clinical outcomes, so the pooled processing approach was used for practical and economic reasons (less processing time, lower costs associated with use of one expensive system versus two).